High-speed video shows how the cat gets the cream

Drinking from a receptacle is no mean feat. Humans get around this
by tilting a glass or sucking up their drink through a straw. But for
our feline friends, it's a tougher challenge.

Now Pedro Reis and his team from the Massachusetts Institute of Technology have filmed cats as they lap up milk to
see precisely how they do it (see video above). The video has revealed
that it's a battle between inertia - how much a substance resists other
forces - and gravity.

"Almost everyone has observed a domestic cat lap milk or water. Yet,
casual observation hardly captures the elegance and complexity of this
act, as the tongue's action is too fast to be resolved by the naked
eye," writes Reis.

The high speed footage allowed the team to look at the tongue's
action in greater detail. They discovered that cats dip their tongue
in, bending it into an inverted "J" shape so the top touches the liquid
but never breaks the surface. A column of liquid is created when the
tongue is retracted, and the cat quickly snaps its mouth shut around the
liquid before it falls back down.

The team also found that the famously rough texture of the cat's
tongue isn't used for lapping. Video footage revealed that only the tip
of the tongue - which is smooth and without any hair-like structures -
is used to drink.

To better understand the fluid dynamics at work, Reis and his team
also created a mechanical model to mimic the lapping motion. They found
that liquid ended up in the cat's mouth thanks to a delicate balance
between inertia, acting on the liquid as it sticks to the tongue and
travels towards the cat's mouth, and gravity, pulling the liquid back
towards the bowl.

"The amount of liquid available to capture each time the cat closes
its mouth depends on the speed and size of the tongue," says Jeffrey
Aristoff, who was part of the team. Bigger cats with larger tongues
should then lap more slowly.

Along with elephant trunks and octopus arms, understanding soft
structures like a cat's tongue can lead to better design of soft robots
and biomechanical models, say the authors.